Vapor separating units are incorporated with internal combustion engines to remove vapor from the fuel supply system. The typical separating unit is located in the fuel line between the fuel tank and the engine, and includes a tank or container into which the fuel is pumped. The liquid level is maintained within the vapor separating tank by a float or other liquid level control mechanism. With fuel injection engines, the fuel is pumped from the vapor separating tank to a fuel rail assembly where the fuel is fed through fuel injectors to the cylinders of the engine. With this system, excess fuel not fed through the fuel injectors is returned either to the fuel tank or in the case of marine engines, the excess fuel is returned to the vapor separating tank.
The fuel rail assembly includes a pressure regulator and as the fuel passes through the regulator, the pressure is reduced. This decrease in pressure can cause vaporization of the fuel. To vent the vapor from the fuel being returned to the vapor separating tank, a vent mechanism is incorporated with the tank to vent the vapor when the vapor pressure exceeds a predetermined value.
Some fuel supply systems utilize a single pump to pump the fuel from the fuel tank through the vapor separating tank-to the engine while other feed systems incorporate a pair of pumps, including a mechanical diaphragm or electric pump to feed the fuel from the fuel tank to the vapor separating tank and an electric pump to feed the fuel from the separating tank to the engine.